With the accelerating growth of Internet and intranet communication, high-bandwidth applications (such as streaming video), and large information databases, the need for networked storage systems has increased dramatically. System performance, data protection, and cost have been some of the main concerns in designing networked storage systems. In the past, many systems have used fibre channel drives because of their speed and reliability. However, fibre channel drives are very costly. Integrated drive electronics (IDE) drives are much cheaper in terms of dollars-per-gigabyte of storage; however, their reliability is inferior to that of fibre channel drives. Furthermore, IDE drives require cumbersome 40-pin cable connections and are not easily replaceable when a drive fails. Serial advanced technology attachment (SATA) drives that use the same receptor as their fibre channel counterparts are now available. These drives, therefore, have the speed required for acceptable system performance and are hot-swappable, meaning that failed drives are easily replaced with new ones. Furthermore, they provide more storage than do fibre channel drives and at a much lower cost. However, SATA drives still do not offer the same reliability as fibre channel drives. Thus, there is an industry push to develop high-capacity storage devices that are low cost and extremely reliable.
To improve data reliability, many computer systems implement a redundant array of independent disk (RAID) system, which is a disk system that includes a collection of multiple disk drives that are organized into a disk array and managed by a common array controller. The array controller presents the array to the user as one or more virtual disks. Disk arrays are the framework to which RAID functionality is added in functional levels to produce cost-effective, highly available, high-performance disk systems.
In RAID systems, the data is distributed over multiple disk drives to allow parallel operation, and thereby enhance disk access performance and provide fault tolerance against drive failures. Currently, a variety of RAID levels from RAID level 0 through RAID level 6 have been specified in the industry. RAID levels 1 through 5 provide a single drive fault tolerance. That is, these RAID levels allow reconstruction of the original data, if any one of the disk drives fails. It is quite possible, however, that more than one SATA drive may fail in a RAID system. For example, dual drive failures are becoming more common as RAID systems incorporate an increasing number of less expensive disk drives.
To provide, in part, a dual-fault tolerance to such failures, the industry has specified a RAID level 6. The RAID 6 architecture is similar to RAID 5, but RAID 6 can overcome the failure of any two disk drives by using an additional parity block for each row (for a storage loss of 2/N). The first parity block (P) is calculated by performing an exclusive or (XOR) operation on a set of positionally assigned data sectors (e.g., rows of data sectors). Likewise, the second parity block (Q) is generated by using the XOR function on a set of positionally assigned data sectors (e.g., columns of data sectors). When a pair of disk drives fails, the conventional dual-fault tolerant RAID systems reconstruct the data of the failed drives by using the parity sets. The RAID systems are well known in the art and are amply described, for example, in The RAIDbook, 6th Edition: A Storage System Technology Handbook, edited by Paul Massiglia (1997), which is incorporated herein by reference.
An example dual parity algorithm is found in U.S. Pat. No. 6,453,428, entitled, “Dual-drive fault tolerant method and system for assigning data chunks to column parity sets.” The '428 patent describes a method of and system for assigning data chunks to column parity sets in a dual-drive fault tolerant storage disk drive system having N disk drives, where N is a prime number. Each of the N disk drives is organized into N chunks, such that the N disk drives are configured as one or more N×N array of chunks. The array has chunks arranged in N rows from row 1 to row N and in N columns from column 1 to column N. Each row includes a plurality of data chunks for storing data, a column parity chunk for storing a column parity set, and a row parity chunk for storing a row parity set. These data chunks are assigned in a predetermined order. The data chunks in each row are assigned to the row parity set. Each column parity set is associated with a set of data chunks in the array, wherein row m is associated with column parity set Qm, where m is an integer that ranges from 1 to N. For row 1 of a selected N×N array, a first data chunk is assigned to a column parity set Qi, wherein i is an integer determined by rounding down (N/2). For each of the remaining data chunks in row 1, each data chunk is assigned to a column parity set Qj, wherein j is an integer one less than the column parity set for the preceding data chunk and wherein j wraps to N when j is equal to 0. For each of the remaining rows 2 to N of the selected array, a first logical data chunk is assigned to a column parity set Qk, wherein k is one greater than the column parity set for the first logical data chunk in a preceding row and wherein k wraps to 1 when k is equal to (N+1). For each of the remaining data chunks in rows 2 to N, each data chunk is assigned to a column parity set Qn, wherein n is an integer one less than a column parity set for the preceding data chunk and wherein n wraps to N when n is equal to 0.
The algorithm described in the '428 patent safeguards against losing data in the event of a dual drive failure. However, performing the algorithm described uses excess processing cycles that may otherwise be utilized for performing system storage tasks. Hence, the '428 patent describes a suitable dual parity algorithm for calculating dual parity and for restoring data from a dual drive failure, yet it fails to provide an optimized software system that is capable of performing the dual parity algorithm without affecting system performance. Furthermore, the algorithm described in the '428 patent is dependent on row and column parity, which may not be the most efficient algorithm for every parity update. There is, therefore, a need for an effective means of calculating parity, such that the storage system is fault tolerant against a dual drive failure, provides optimal performance by an algorithm that runs a priori, and, further, is capable of generating parity regardless of symbol position (i.e., not dependent on row, diagonal/column parity).
It is therefore an object of the invention to provide an algorithm that compensates for dual-storage element failures in a networked storage system.
It is another object of this invention to provide an algorithm that compensates for dual-storage element failures in a networked storage system and that is not dependent on symbol position.
It is yet another object of this invention to provide an algorithm that compensates for dual-storage element failures in a networked storage system and that runs once a priori.